The present invention relates to a motor torque control system for a vehicle equipped with a drive torque generating motor.
Electric vehicles and hybrid electric vehicles are capable of freely controlling a motor torque, and therefore there are capable of stopping the generation of the motor torque when the vehicle stops running to decrease the energy consumption. Further, when the hybrid electric vehicle stops running, an idling stop for stopping an engine is executed and the generation of the motor torque is also stopped to decrease the energy consumption. That is, these electric vehicle and hybrid electric vehicle do not generate a creep torque caused by an idling engine revolution although such a creep torque is normally generated by a vehicle equipped with a known automatic transmission with a torque converter. On the other hand, such a creep torque enables an extremely low speed running available for parking a vehicle at a predetermined space and running the vehicle in a traffic jam, and enables suppressing a back movement during a starting on an upslope. Therefore the utilization of creep torque improves a drivability. Since the great majority of vehicles have functions of a creep running, almost drivers feel that a creep running of a vehicle is an essential function.
Although a creep running of an electric vehicle or hybrid electric vehicle is effectively executed by driving a motor, generation of a motor torque under a brake depression state uselessly consumes electric power. Therefore, it is preferable that the generation of the motor torque becomes zero under the brake depression state. However, this method has a possibility of generating a back movement on a sheep upslope if a generation of a creep torque just after the brake releasing is delayed.
Japanese Published Patent Application No. 2001-103618 discloses a control system of achieving both of decreasing an electric power consumption and an upslope starting performance, by decreasing the motor torque according to the increasing of a depression quantity of a brake.